During the mid–nineteenth century, when vendors sold popcorn on the streets and at fairs, circuses, and sporting events. The popcorn industry began in the latter part of the nineteenth century. Popcorn was not sold in movie theaters until the Great Depression, when owners found that they could make more money on popcorn and other snack food sales than they did on theater admissions. The selling of ready-to-eat popcorn in large bags began before World War II, and sales have increased ever since. The invention of the microwave oven increased popcorn sales and profits to even greater heights.